Modulated RF generator. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Radio amateur designer
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A diagram of a simple generator, in which both amplitude and frequency modulation of the RF signal can be performed, is shown in the figure. Frequency modulation is carried out in an LC circuit with a varicap - VD1, C5, C6, L1, and amplitude modulation - by linear control of the current VT2 and, accordingly, the transistors VT1 and VT3 of the generator. Transistor VT2 works as an amplitude modulator. The device for introducing the FM is simplified as much as possible on the assumption that the slider of the resistor R5 will not be set to its extreme positions. If such a case is possible during operation, then it is necessary to turn on limiting resistors with a resistance of 1,5 ... 2 kOhm at the points marked with crosses in the diagram.
In the case when the FM mode is not needed in the generator, the elements C1, C4, C5, R5, R6, VD1 are excluded. If there is no need for AM mode, then R1, R2, R7, C2, VT2 are excluded, and the emitters of transistors VT1 and VT3 are connected together by connecting through a resistor R9 to a common wire.
In the generator, you can use any high-frequency transistors pnp or npn structures by choosing the appropriate polarity of the supply voltage, as well as the polarity of the inclusion of capacitors C1, C2 and varicap VD1. For example, silicon transistors of the KT312, KT315, KT361 series, germanium transistors - GT309, P422, P401 and similar ones in terms of parameters work well in the generator. Resistors - MLT-0,125, and R5 - any small trimmer. Varicap - D901 series or similar (depending on the frequency range), Zener diodes of the D814 series can also be used. Polar capacitors C1 and C2 - K50-12, K50-35 or other oxide for a voltage of 12 V and above, the rest are ceramic.
The parameters of the capacitor C6 and the inductor L1 depend on the frequency of the generator. For example, with a capacitance C6 of 750 pF and an inductor L1 wound on a ferrite rod 30 mm long, 8 mm in diameter and containing 65 turns of PEL-1 wire 0,1 mm, the generator frequency is approximately 430 ... 500 kHz. Coil L2 (6 turns with the same wire) is wound next to L1.
Author: D.Ataev, Sterlitamak, Bashkortostan
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